Recently, as smart phones and tablet personal computers (PCs) have entered widespread use and high-capacity multimedia communication have been actively used, mobile traffic has remarkably increased. In the future, it is expected that mobile traffic will double every year. Most mobile traffic is transmitted through a base station (BS). Thus, communication service carriers are currently faced with serious problems in terms of network load. Thus, in order to process increased traffic, communication carriers have increased the number of network facilitates and have hurriedly commercialized next-generation mobile communication standards for effectively processing a large amount of traffic, such as mobile world interoperability for microwave access (WiMAX) and long term evolution (LTE). However, at this time, other solutions are needed to cope with dramatic increase in wireless traffic in the future.
Device-to-device (D2D) communication refers to distributed communication technology for directly transmitting traffic between adjacent nodes without infrastructures such as a BS. In a D2D communication environment, each node such as portable user equipment (UE) and so on searches for another UE that is physically adjacent thereto, establishes a communication session therewith and then transmits traffic. Likewise, D2D communication distributes traffic concentrated at a BS to overcome traffic overload problems and thus, has drawn attention as the next-generation mobile communication technology successor to 4G. For this reason, standard institutes such as the 3rd generation partnership project (3GPP), the institute of electrical and electronic engineers (IEEE), and the like have established D2D communication standards based on long term evolution-A (LTE-A) or wireless-fidelity (Wi-Fi), and Qualcomm and so on have also developed unique D2D communication technologies.
D2D communication is predicted to create new communication services as well as to increase performance of mobile communication systems. In addition, D2D communication can support services such as an adjacency-based social network service, a network game, or the like and can overcome problems in terms of connection of UEs in a shadow region using a D2D link as a relay. Thus, D2D technologies are predicted to provide new services in various fields.
In reality, technology for communication between devices, such as infrared communications, ZigBee, radio frequency identification (RFID), and near field communication (NFC) based thereon have already entered widespread use. However, these technologies only support communication with one partner within a very limited distance (about 1 m). Thus, strictly, it is difficult to classify these technologies as D2D communication technologies for distributing traffic of a BS.
Thus far, D2D communication has been described. However, until now, details of network-assisted D2D for implementing D2D communication with the help of a cellular network have not been proposed.